1. Technical Field
The present invention relates to an electronic component and a manufacturing method for an electronic component.
2. Related Art
A semiconductor device having a package structure where a semiconductor element is bonded with a circuit pattern disposed on an insulated substrate has been proposed. As a method of bonding an electrode disposed on a front surface of a semiconductor element (hereafter called “front surface electrode”) with the circuit pattern of the insulated substrate, a method of using an aluminum (Al) wire or solder for bonding is known. FIG. 11 is a cross-sectional view depicting a main section of a semiconductor device having a conventional package structure. As shown in FIG. 11, the rear surface of a semiconductor chip 101 having a semiconductor element is bonded with a circuit pattern 104 on the front surface of an insulated substrate 103 via a solder bonding layer 102.
The rear surface of the insulated substrate 103 is bonded with the front surface of a metal plate formed of copper (Cu) (hereafter called “Cu plate”) 105, for example. The rear surface of the Cu plate 105 is bonded with the front face of a base material 106 via a solder bonding layer (not illustrated). A front surface electrode (not illustrated) of a semiconductor element disposed on the front surface of the semiconductor chip 101 is connected with an aluminum wire 107 by thermo-compression bonding or by ultrasonic vibration, and is electrically connected with the circuit pattern 104 via the aluminum wire 107.
FIG. 12 is a cross-sectional view depicting a main section of another example of a semiconductor device having a conventional package structure. As shown in FIG. 12, a front surface electrode (not illustrated) of a semiconductor chip 101 is electrically connected with a circuit pattern 104 via a metal plate 108. The front surface electrode and the circuit pattern 104 are bonded with the metal plate 108 respectively via a solder bonding layer 102. The configuration of the semiconductor device in FIG. 12, excluding the metal plate 108, is the same as the semiconductor device in FIG. 11. In FIG. 11 and FIG. 12, a case and a terminal for an external electrode are not illustrated.
The front surface electrode of the semiconductor element is made of aluminum or aluminum alloy, for example. However aluminum has poor wettability to solder and therefore cannot firmly adhere to solder. To solve this problem, an under-bump metal film, which has high adhesion to the front surface electrode and to the solder, must be formed between the front surface electrode and the solder bonding layer. For the under-bump metal film, normally an electroless Ni/Au plating film (ENIG) is used. By using Ni/Au plating film on the surface of the front surface electrode of the semiconductor element, a firm solder bonding with the front surface electrode becomes possible.
As a method for forming such a plating film, a method of continuously performing a step of contacting a plating target material to an electroless gold plating solution that does not contain gold ions, and a step of contacting the plating target material to an electroless gold plating solution containing gold ions has been proposed. See Japanese Patent No. 3484367 (also referred to herein as “Patent Document 1”).
Another method for applying a plating film on an electronic component that has been proposed is plating a conductive portion formed on a surface of a substrate body, sequentially forming an electroless Ni film of which major component is Ni and a substituted Au film of which major component is Au, and then performing after-treatment to remove the Ni compound adhering to the substituted Au film. In this method, a predetermined complexing agent, selected from citric acid, glycine, acetic acid, gluconic acid, glutamic acid, tartaric acid, ethylenediaminetetraacetic acid, diethylenetriamine pentaacetic acid, malic acid, malonic acid, sulfurous acid, ammonia and sulfamic acid is used as the Ni removing liquid, and in the after-treatment, a contact treatment is performed by contacting the Ni compound with the Ni removing liquid, so as to remove the Ni compound from the surface of the substituted Au film. See Japanese Patent No. 4096671 (also referred to as “Patent Document 2”).
As an electronic component manufactured by another method for applying a plating film, the following electronic component has been proposed. In the electronic component, an Ni—P film which has a double layer structure is formed on a conductive portion which is formed on the surface of a ceramic body, and an Au film is formed on the surface of the Ni—P film. Within the Ni—P film with two layers, the first layer contains 3 to 6 wt % P, and the second layer contains 6 to 9 wt % P, and has a 0.1 μm to 1.0 μm thickness. See Japanese Patent Application Laid-open No. 2006-131949 (also referred to herein as “Patent Document 3”).
As another method for applying a plating film, the following method has been proposed. To apply the plating film, a Cu electrode is formed on a ceramic body via a pre-treatment step, an auto-catalytic Ni plating step and a substituted Au plating step, and on the Cu electrode, an Ni—P film and an Au film are sequentially formed. In the after-treatment step, the ceramic body formed on the Au film is placed in a vacuum drying apparatus where pressure is reduced to 13.3 Pa or less, and a vacuum drying treatment is performed, so as to remove the moisture remaining in the interface between the Ni—P film and the Au film. Instead of the Au film, a metal of which ionization tendency is lesser than Ni, such as Ag, Cu, Pd, Pt or an alloy of these metals, may be used. See Japanese Patent Application Laid-open No. 2004-115902 (also referred to herein as “Patent Document 4”).
As another method for applying a plating film, the following method has been proposed. For the connection terminal, Ni plating is applied to a copper plate, and gold plating is applied thereon. After mounting a semiconductor element on a wiring of an insulated substrate, a solution containing Au particles (average particle diameter: 5 nm) is coated on an emitter electrode (upper side) of the semiconductor element. Ni plating treatment is performed on the surface of a copper wiring pattern formed on the insulated substrate, then Au plating treatment is performed on the portion connecting with the emitter electrode of the semiconductor element via a terminal, and the solution containing Au particles is applied to the Au plated portion of the wiring. The solution containing Au coated on the semiconductor element and the wiring on the insulated substrate is dried and an electrode portion formed of gold particles is formed, then the connection terminal is mounted on the upper part of the electrode formed of gold particles, and an approximately 80° C. heat is applied for 60 minutes so as to connect the semiconductor element and the wiring. See Japanese Patent Application Laid-open No. 2005-136375 (also referred to herein as “Patent Document 5”).
As yet another method for applying a plating film and a method for mounting a semiconductor element on a wiring circuit, the following method has been proposed. A thin nickel layer is formed on a metal layer of a semiconductor element by the electroless plating method, and this thin nickel layer and a wiring circuit are bonded using an anisotropic conductive adhesive. Or after the thin nickel layer is formed, a palladium alloy layer containing 0.1 to 95 wt % palladium and lead or tin is formed by the electroless plating method, and is bonded with the wiring circuit using the anisotropic conductive adhesive. The anisotropic conductive adhesive that is used contains gold, platinum or silver particles having protrusions (particle diameter: 20 μm or less) as a conductive filler, and includes epoxy resin which is mixed as a binder. See Japanese Patent Application Laid-open No. H7-263493 (also referred to herein as “Patent Document 6”).
As another method for applying a plating film, the following method has been proposed. When a semiconductor element is mounted on a lead frame, Ag or Ag alloy plating film is applied to areas where the semiconductor element and the lead frame are bonded, and conductive adhesive containing nano-particles are used for the bonding material for this mounting. The conductive adhesive has a thermo-setting resin, such as epoxy resin, as a base, where silver particles having a 1 to 20 μm particles diameter and silver particles having a 20 nm or less particle diameter are mixed. See Japanese Patent Application Laid-open No. 2007-180059 (also referred to herein as “Patent Document 7”).
As another method for applying a plating film, the following method has been proposed. A step of forming an oxide layer containing oxygen on a bonding interface of a bonding target member, a step of disposing a bonding material containing metal compound particles having a 1 nm to 50 μm average particle diameter, and a reducing agent formed of an organic matter, on the bonding interface, and a step of bonding the bonding target members by heating and pressurizing the area between the bonding target members, are performed. On the bonding surfaces of the bonding target members, a treatment of precipitating copper, silver or nickel by electroless plating or electric plating and oxidizing the surface of the plating metal, has been performed in advance before bonding. See Japanese Patent Application Laid-open No. 2008-208442 (also referred to herein as “Patent Document 8”).
Another method of bonding a front surface electrode of a semiconductor element with a circuit pattern on an insulated substrate, a method of bonding using a bonding layer containing silver (Ag) particles, instead of solder bonding, has recently been proposed. In the bonding method using a bonding layer containing silver particles, metal particles, of which surfaces are coated with such an organic matter as a silver nano-particle bonding material, are used as a bonding material to bond metal surfaces formed by electroless plating or electric plating, so as to implement bonding having high heat resistance, reliability and radiation performance, and thereby the bonding temperature is lowered during bonding in the mounting process (see Patent Document 8).
In the case of bonding using the bonding layer containing Ag particles, the bonding portion between the front surface electrode of the semiconductor element and the bonding layer containing Ag particles must be a precious metal, such as gold or silver (Ag). As mentioned above, the front surface electrode of the semiconductor element is formed of aluminum or aluminum alloy, for example, therefore it is difficult to directly deposit (form) the gold plating film or the silver plating film on the surface of the front surface electrode of the semiconductor element. Hence an Ni/Au plating film or an Ni/Ag plating film, where an Ni plating film is sandwiched by the front surface electrode of the semiconductor element and the gold plating film or the silver plating film, is primarily used.
However after intensive research by the present inventors, it became clear that the following problems exist. In the case of bonding using an aluminum wire or solder where heat resistance is low, and in the case of bonding using conductive adhesive where a heat resistance of epoxy resin used as the binder is low, and a thermal conductivity that is also low, none can provide electronic components that can operate under a high temperature environment (e.g. continuous operation at 175° C.), which are currently in demand. Further, in the case of bonding using conductive adhesive, Ag is used as the conductive filler, but epoxy resin, which is used as the binder, is used for bonding. Therefore the adhesion mechanism is different from the bonding using a conductive composition containing Ag particles, and the characteristics demanded for the bonding target also differs considerably. In the case of using a bonding layer containing Ag particles, heat resistance under the high temperature environment can be implemented. However if the bonding layer containing Ag particles is used for bonding, the bonding strength with the plating metal on the outermost surface of the front surface electrode of the semiconductor element greatly depends on the type and the film thickness of the plating metal, which means that the bonding conditions to acquire high bonding strength must be considered.